The present invention is concerned with a speed reducing and torque increasing device. More particularly, the present invention is concerned with a speed reduction gear arrangement which forms a dynamically balanced speed reducing system having an extremely short torque path. The system of the present invention is capable of large speed reductions in a single stage.
Many grear devices are known in the prior art for reducing the speed of an input shaft. In some speed reducing devices, particularly those developed earlier in the art having conventional involute gears, the gears are arranged so that only one or two teeth of each gear are in mesh at any one time, giving rise to various problems of vibration, gear wear and lost motion as these few teeth are required to absorb the entire shock of overload and stress on the gears.
In other known speed reducing devices, eccentric means is provided in combination with various types of inner ring assemblies, such devices providing for a larger number of teeth of each engaged gear to be in engagement at any time during rotation of the gear. Speed reducing devices of the latter type are described, for example, in U.S. Pat. No. 3,429,393 to Lorence. Such prior art devices, while representing an improvement over conventional involute gear systems, are also characterized by excessive noise and vibration in operation.
By the present invention, there is provided a speed reducing device which has been found to overcome many of the disadvantages associated with speed reducing systems of the prior art. The speed reducing system of the present invention operates on a novel concept to produce a large mechanical advantage between axial aligned input and output components. As a result of the characteristics inherent in this novel construction, the reduction gear system of the present invention offers numerous operating advantages in the field of high-ratio mechanical power transmission. The present system has been found to maintain an effeiciency of up to 98%, with the result that the present system offers definite advantages in the area of energy conservation.
The speed reducing system of the present invention includes input and output shafts which are in axial alignment. An eccentric member and a counterweight are carried by the input shaft. A fixed gear spline is positioned on the interior of the cover on the input side and a rotatable output gear spline is positioned on the interior of the casing on the output side. Between these two splines there is mounted for eccentric rotation on the input shaft a transformer gear component which includes a pair of spur gears having a common axis.
One gear of the pair of spur gears which comprise the transformer is in engagement with the fixed spline while the other gear is in engagement with the output spline. In accordance with the choice of nomenclature which denotes the interior gear component as a transformer, the first spur gear, in engagement with the fixed spline, is described herein as the primary transformer gear, and the second spur gear, in engagement with the output spline, is denoted the secondary transformer gear.
The primary gear has a smaller number of teeth than the fixed gear spline, with which the primary gear is in engagement, while the secondary gear has a smaller number of teeth than the output gear spline, with which the secondary gear is in engagement. Rotation of the input shaft with its eccentrically mounted transformer gear unit causes the primary and secondary gears to rotate in unison in a direction opposite to the direction of rotation of the input shaft. Such rotation of the primary and secondary gears, in turn, results in the output shaft being rotated in a direction which depends upon the relationship between the number of teeth of the primary and secondary gears. If the primary gear has a greater number of teeth than the secondary gear, the output shaft will rotate in the same direction as the direction of rotation of the input shaft, while the output shaft will rotate in a direction opposite to that of the input shaft when the primary gear has a smaller number of teeth than the secondary gear. The counterweight is formed integrally with or attached to the eccentric, with the counterweight extending from the input shaft in a direction diametrically opposite to the eccentric, thus providing a dynamically balanced system which is mandatory, particularly for high speed applications.
The eccentric and counterweight elements may be positioned on the input shaft with bearings on either side or, alternatively, the eccentric and counterweight may be located at the outer end of the input shaft with bearings located interiorly of the eccentric and counterweight along the input shaft. In this latter configuration, the eccentric and counterweight assume a cantilevered configuration in conjunction with the input shaft. The eccentric may be formed integrally either with the input shaft or with the combination of the input shaft and counterweight or, alternatively, the eccentric may be constructed separately and attached by bolts or similar means to the shaft as an assembled component. In a similar manner, the counterweight may either be formed integrally with the input shaft, or constructed separately and assembled onto the input shaft. As aother alternative, the counterweight and eccentric may be formed integrally as a single unit and pinned or keyed to the input shaft.
The primary and secondary transformer gears may be formed with either the primary or secondary gear having the greater number of teeth, with the direction of rotation of the output shaft relative to the direction of rotation of the input shaft varying accordingly, as previously discussed. These transformer gears may either be formed integrally or constructed separately and secured together by suitable means such as welding, screws, bolts, rivets or pins. A cavity for rotation of the counterweight may be located within the system either between the primary and secondary gears as an internal cavity or on one or both sides of the transformer gears as external cavities. Either a single or double cover or bell may be employed to cover the system.
The relationship of the rotatable output gear spline with the output shaft is such that these two elements may be formed integrally as a single piece or, alternatively, the two components may be constructed separately and assembled by bolts or other suitable means. It may be desirable in some situations to employ an output case rather than an output shaft. The use of an output case is advantageous in conjunction with the timing belt, V-belt, chain sprocket or cable drum. When an output shaft is employed, the shaft may be constructed with a keyway or slot, for example, or the shaft may be either splined, tapered to a conical shape along its longitudinal axis, or constructed as a hollow member with a splined interior surface. Either conventional bearings or peripheral bearings may be employed to allow rotation of the output shaft or case relative to the other components, although peripheral bearings are preferred, as described hereinafter.
The fixed gear spline may be formed integrally with the cover for the system or, alternatively, the fixed gear spline and cover may be constructed separately and secured to each other by bolts or similar securing means. The cover may be secured to an external casing or connected through bearings to the output portion of the system.
In the use of the speed reducing device of the present invention, speed reductions of the order of 40:1 up to several thousand :1 and greater are obtained in a single stage. A particularly distinctive feature of the speed reducing system of the present invention is the short, compact, stiff torque path, which extends in the present system from the fixed gear spline through the periphery of the primary and secondary gears to the output gear spline. The interrelationship of the various components results in a speed reducer of remarkable compactness and exceptionally high mechanical efficiency. Furthermore, there is virtually no noise or vibration in the present system, with the result that backlash is substantially reduced. Such advantages are attributable, at least in part, to the preferred 30 degree contact pressure angle at the gear teeth, such an angle providing distinct advantages over conventional teeth having contact angles such as 141/2.degree. and 20.degree..
A particularly unique feature of the present invention is that only a very small portion of the system comes under stress at any one moment. Because of the shortness of the torque generating path and because immediate support is provided at all possible points of stress existing around the periphery of the system, it is possible to eliminate metallic deflections and to reduce noise and vibration inherently associated with this phenomenon down to a bare minimum. Also, since the torque path is almost at the periphery of the system, taking advantage of the most favorable mechanical leverage, i.e., higher foot pound value, it is advantageous to have the bearing system also located at the periphery.
The peripheral bearing system, on which is mounted the output transmitting member of the system, is placed in a direct straight line with the lines of force transferred by the few gear teeth which are in mesh. Thus, this bearing system is well placed to support the stressed teeth in an adjacent position. Long mechanical linkages that would give and flex have therefore been eliminated.
The advantages obtained by the use of peripheral bearings versus a conventional shaft bearing include the fact that, if a peripheral bearing has a diameter four times greater than the diameter of a shaft bearing, then the loading capacity of the peripheral beaing is also at least four times greater than that specified for the shaft bearing. In this way, the output system using a peripheral bearing is rated for a much greater torque than would otherwise be possible with conventional shaft bearings. Also, large centilevered loadings can exist when a pully or a winch is mounted on the output system and these can be handled by a single peripheral bearing. Normally the same function would require two bearings mounted far apart on the same shaft. As a rule, single shaft bearings will tolerate no cantilevered loading. Furthermore, the peripheral bearing provides advantages of compactness and load distribution compared to conventional shaft bearings.